As is generally known the prostate is located at the base of the bladder, where it surrounds a portion of the urethra, the tube connecting the bladder and the outside world. The function of the prostate is to produce a fluid which becomes a part of the ejaculated semen (which is carried through the urethra). As men grow older, the tissue of the prostate often begins to enlarge, a condition known as hyperplasia. As the bulk of the prostate enlarges, the gland begins to constrict the portion of the urethra passing through the prostate and thus prevent the normal flow of urine, a condition known as benign prostatic hypertrophy or hyperplasia (BPH). As BPH develops, one or more constricted or stenotic regions within the prostatic urethra can from time to time obstruct the flow of urine; so the signs of BPH are difficulty starting urination, dribbling following urination, reduced force of the stream of urine, a tendency to urinate frequently in small amounts as well as pain and discomfort. As a result an increase in urinary tract infections can occur. The symptoms are common, 75-80% of men over the age of fifty are affected. See, for example, the Harvard Medical Health Letter; September 1988; Volume 13; Number 11; pages 1-4 and Castaneda, Flavio et al.; "Prostatic Urethra: Experimental Dilation in Dogs"; Radiology; June, 1987; pp. 645-648. In fact recent statistics apparently reveal that a 50 year old man has a 20-25% chance of undergoing treatment for this condition during his lifetime. See Casteneda et al., suora; and PCT International Published Application 90/13333.
When the obstructive symptoms of BPH become bothersome, the constricted portions of the urethra are usually reopened surgically. Current accepted treatment for BPH involves either open or transurethral surgery, which is costly and is associated with an acceptable but undesirable degree of mortality (estimated from 1.3% to 3.2% see Castaneda, Flavio et al.; "Benign Prostatic Hypertrophy: Retrograde Transurethral Dilation of the Prostatic Urethra in Humans" Radiology; June, 1987, pp. 649-653), and with a significant degree of morbidity, especially with less fit patients.
The most common surgical procedure for BPH, as an alternative to open surgery, is a transurethral resection of the prostate, or TURP. The transurethral resection involves inserting a resectoscope through the urethra. A spring wire, adapted to carry an electric current, is inserted through the resectoscope for use in removing tissue. The wire carries one current for cutting away "chips" of tissue with the resectoscope and another current for cauterizing the remaining tissue to minimize bleeding. As much as two cubic inches of tissue are removed in this way.
The TURP surgical technique is not trivial nor inexpensive, though the actual procedure can ordinarily be done within one hour. The procedure carries similar risks as many of those associated with other general surgical procedures. In addition, intraoperative irrigation fluids are required to flush blood from the prostatic urethra while tissue is being removed creating a danger that the flushing fluid will enter the blood circulatory system through iatrogenic openings into veins causing fluid overload and possible death, a result known as "post-TURP" syndrome. Other surgical hazards include stricture formation at the urethra or bladder neck, post-manipulation pain or bladder spasm, urinary tract infections, and reactive urethral swelling which can cause urinary obstruction and epididymitis. Other complications include retrograde ejaculation and delayed recurrent obstruction of the bladder neck area. Further, the post-operative care following a TURP procedure requires a prolonged hospital stay, creating substantial costs for medical care. The appropriate DRG (Diagnostically Related Group), currently designated by Medicare, for the TURP procedure presently entails an average length of hospital stay of 5.8 days. Accordingly, current pressures exist to reduce allowable Medicare fees for the TURP procedure and the impact of such reduced fees on urological patient care and the American urologist. In addition, some men have reported sexual dysfunction following a resection. Certain men have also become incontinent as a result of the surgery because of inadvertent damage done to the external sphincter muscles positioned at the apex of the prostate for controlling urine flow. The surgery usually results in moderate discomfort with some post-operative bleeding being usual.
As a result of the trauma that many men experience from TURP and the relatively long in-patient care required for post operative recovery, alternative techniques of treating BPH are being investigated. For example, recent attention has been given to laser surgery to relieve obstruction. See, for example, U.S. Pat. No. 4,672,963 issued to Dr. Israel Barken, and Smith, Jr., Joseph A. et al.; "Laser Photoradiation in Urologic Surgery"; The Journal of Urology; Vol. 31, April, 1984, pp. 631-635, cited therein. Also see PCT Published Application No. WO 90/13333.
Other alternatives of open prostatectomy and the TURP procedure and open prostatectomy include long-term hormone treatments with, for example, alpha-adrenergic blockers, enzymes (e.g., 5 alpha-reductase inhibitors), or antiandrogens, in order to prevent or reverse prostate enlargement. However, there have been some uncertainties about the role played by hormones in creating BPH. Transurethral incision of the prostate (TUIP) is another approach, although its risks are not much different from the TURP procedure. A device for transrectally applying thermal therapy to the transitional zone of the prostatic urethra with microwave energy is being marketed by the Armonite, Inc. of NY. The long term results of such therapy are currently inconclusive.
Finally, balloon dilatation of the prostatic urethra has received a great deal of recent attention with the development of dilatation balloon technology. In this latter approach a catheter having an inflatable non-compliant balloon positioned at the distal end of the catheter is transurethrally inserted into the prostatic urethra. The balloon is then inflated so that the expanding balloon dilates the urethra and is held in its inflated state for a limited period of time, e.g., between ten and sixty minutes. See, for example, Castaneda, et al. "Prostatic Urethra: Experimental Dilation in Dogs"; Radiology; June, 1987, pp. 645-648; and Castaneda, et al.; "Benign Prostatic Hypertrophy: Retrograde Transurethral Dilation of the Prostatic Urethra in Humans"; Radiology; June, 1987; pp 649-653. See also U.S. Pat. No. 4,660,560 issued to Klein; Astra Urologue, Astra Pharmaceutical Products, Inc. Westborough, MA, May 1990, pp 1-8; and Dowd, Joseph B. et al., Ed., "Balloon Dilatation of the Prostate, Concept and Technique" Microvasive Education Center, Boston Scientific Corporation, Boston, MA. During the balloon dilatation procedure the tissue of the prostatic urethra must be expanded beyond its normal elastic limit, otherwise the urethra will not remain dilated for very long since the tissue will rebound to a certain extent. Accordingly, the balloon is sized to expand, for example, to a 25 mm to 30 mm diameter so as to cause the tissue within the averaged sized prostate to stretch to the point of actually tearing or cracking so that when the tissue heals, permanent fissures will remain so that urethra will remain dilated. Such a procedure will not always insure long term effects of relieving the stenosis and constriction of the urethral walls due to the nature of the resilient muscle tissues and large bulk of the hypertrophied prostate which has a tendency to rebound after temporary compression. Accordingly, as described in U.S. Pat. No. 4,762,128 issued to Rosenbluth, the latter proposes to insert a stent in the prostatic urethra after being dilated by the balloon and remove the stent at a later time, although the stents are difficult to remove once they have been inserted and create a tendency for irritation and encrustation.
While all of these procedures have advantages, at the present time sufficient data do not exist that suggest one "best" alternative. However, of the alternative approaches, balloon dilatation seems to be one of the safer, more proven approaches for providing at least short term relief for urinary outflow obstruction.
Historically, as early as mid-nineteenth century, a number of instruments were specifically developed to dilate the prostatic urethra and bladder neck. The most widely used was a metal dilator designed by Mercier in 1850. In 1910, tranvesical digital dilatation of the bladder neck and prostate was described. This technique was performed through a small suprapubic cystotomy and was associated with lower morbidity and mortality than the open prostatectomy. In 1956, Deisting and Frank developed a metal dilator that was a modification of Mercier's design. Using a retrograde transurethral approach, the metal dilator was positioned across the prostate. Correct position was confirmed by rectal digital palpation. When opened, the dilator would disrupt the anterior and posterior prostatic commisures. The use of dilatation techniques as an alternative to open prostatectomy began to wane as the use of the TURP began to increase. However, recent studies questioning the safety and efficacy of TURP and the development of improved balloon technology for such purposes have rekindled interest in the transurethral balloon dilatation procedure.
When performing a balloon dilatation procedure of the prostate, it is most important that steps are taken to insure that the inflatable balloon is properly positioned within the prostatic urethra during the procedure. In fact of all the variables of balloon design and operative technique, proper placement of the balloon relative to the apex of the prostate is most critical, both at the beginning and during the entire inflation period. In accordance with at least one approach, the length of the balloon is chosen based upon the premeasured size of the prostatic urethra so that the external urethra and bladder neck are not damaged while the balloon is inflated. If the balloon is too large or is incorrectly positioned within the prostatic urethra so that a portion of the balloon inflates in the external sphincter at the apex of the prostate, for example, the sphincter and apex may be damaged in such a manner as to cause incontinence. Accordingly, care must be taken to measure the location and size of the prostate before performing this dilatation procedure. One of the earliest attempts to visualize placement of the balloon was accomplished by placing radioopaque markings on the catheter so that the markings could be observed fluoroscopically as the balloon catheter was inserted into the prostate under X-ray control. Although the early results were encouraging, the fluoroscopic approach requires the cooperation of a radiologist, creating unnecessary scheduling and cost problems, and alone was not always sufficiently precise in providing localization of the dilatation balloon within the prostatic urethra.
Another instrument for performing prostatic balloon dilatation is the Dowd.TM. Prostatic Balloon Dilatation Catheter manufactured by Microvasive, an affiliate of Boston Scientific Corporation of Boston, MS. The latter in Dowd, Joseph B., et al.; "Balloon Dilatation of the Prostate", published at the A.U.A. meeting in New Orleans, LA, May 12-17, 1990, includes an inflatable, substantially non-compliant balloon (typically made of polyethylene terephthalate), positioned on the distal end of a catheter. The catheter is adapted to be transurethrally inserted through the urethra so that the balloon is located in the portion of the urethra extending through the prostate. The balloon is then inflated, typically to a pressure of about four atmospheres, so that the expanding balloon dilates the urethra and is held in its inflated state for a limited period of time, e.g., about ten minutes. The balloon is sized to expand to a 30 mm diameter (90 F) giving fairly good results, better than a smaller 75 F balloon.
The Dowd.TM. Dilation Ctheter utilizes a single balloon having an effective dilating length of 5 cm to ensure adequate dilation of both the prostatic capsule along the full length of the prostatic urethra as well as the bladder neck. The proper balloon position however is accomplished by transrectal digital palpation. Specifically, a 19 F positioning nodule is provided on the catheter proximal to the balloon so as to permit precise placement using transrectal digital control. This assumes, however, that by transrectally sensing the nodule at a certain position, the balloon will be properly positioned distal to the apex of the prostate. However, the anatomy of prostate can not be precisely felt transrectally, i.e., the location of the apex of the prostate and external sphincter may not be where the physician believes it to be, and may in fact move with the insertion of the balloon catheter and even deform with balloon dilatation.
Another approach utilizes a trans-cystoscopic technique, described in the Astra Urologue publication, supra, and in U.S. Pat. No. 5,007,898 and Klein, Lester A., "Transcystoscopic Balloon Dilatation of the Prostate", published at the A.U.A. meeting in New Orleans, LA, May 12-17, 1990. The approach described in the later apper, as well as U.S. Pat. No. 4,660,560 involves the insertion of a standard cystoscope into the prostatic urethra. The cystoscope includes a metal sheath and an optic. The latter is an instrument for optically viewing the prostatic urethra intralumenally and is adapted to slide into the sheath and lock into but a single position at the end of the sheath. The cystoscope is used to evaluate the prostate and surrounding structures. By moving the entire instrument along the urethra, the bladder is usually inspected for incidental pathology and the external sphincter is clearly located so as to avoid damaging the latter. A separate, specially designed measuring catheter, with calibration markings provided at predetermined axial intervals (e.g. 1 cm spacings) with an inflatable balloon located at its end, is next inserted through the cystoscope, and secured beyond the end of the cystoscope at the bladder neck with the inflatable balloon. The distance between the bladder neck and the external sphincter is determined with the cystoscope, which is moved along the urethral passageway relative to and external of the calibration catheter, by viewing the calibration markings on the latter device. A plurality of catheters, provided with various length-sized balloons, are made available so that based on the measurement obtained, the proper balloon length can then be chosen. The chosen balloon catheter is then inserted into the prostatic urethra via the cystoscope. At the end of the balloon catheter is a Foley balloon that is inflated beyond the distal end of the cystoscope, within the bladder before the inflation of the dilatation balloon so as to anchor the dilatation balloon in its proper position within the prostatic urethra. A localization band on the balloon catheter is provided a predetermined distance, e.g., 0.5 cm, from the dilatation balloon, distal to the external sphincter and assists in the proper positioning of the dilatation balloon relative to the apex of the prostate. This band is then visualized just distal to the external sphincter within the prostatic urethra (with the external sphincter being visualized as well) through the specially designed cystoscope which is moved within the urethra to a position where the band is in view just distal from the distal end of the cystoscope and external of the balloon catheter. In this technique the bladder neck is not dilated.
During the dilatation process (i.e., the inflation of the balloon), the view of the dilatation balloon and prostate is obscured, so that the urologist relies on the localization band to ensure that the balloon catheter is properly positioned before the balloon is inflated. The dilatation catheter contains an irrigation channel allowing visualization and irrigation. Once the positioning of the balloon is confirmed, the balloon is inflated to its inflated dimensions at the inflated pressure (e.g., 3 atmosphere) for the predetermined time (e.g., 10 minutes) for providing the dilatation of the prostatic urethra. Since the balloon has a tendency to move toward the bladder as it is inflated, the localization band (and thus indirectly the balloon) is monitored by the cystoscope to insure that the balloon does not move. Once inflated, if the dilating balloon is correctly positioned it does not usually migrate since the bladder neck is trapped between the two inflated balloon. After the time period of balloon inflation passes, the balloons are deflated and withdrawn through the cystoscope. Withdrawing the balloon through the cystoscope protects the urethra from being traumatized by the balloon.
While the above cystoscopic measurements work reasonably well in providing the proper size of and position for the balloon, the use of multiple instruments makes the procedure more cumbersome and time consuming and difficult for the patient. Continual monitoring of the localization band with the cystoscope creates a less accurate positioning technique due to the fact that it is indirectly related to the actual positions of the landmarks of the prostate and ignores any possible movement of the cystoscope itself.